Emitter geolocation methods exist that rely either on use of multiple separate simultaneous signal collection platforms (e.g., separate aircraft), or rely on knowledge of the signal modulation structure of an emitter signal. For example, a direct approach to geolocation that requires knowledge of emitter signal modulation has been conventionally employed. Such a direct approach does not require determination of an intermediate geolocation observable measurement such as from time difference of arrival (TDOA), frequency difference of arrival (FDOA), direction of arrival (DOA), etc. However, such a conventional direct geolocation approach requires and relies on prior knowledge of some or all of the emitted signal (e.g., a known reference signal embedded in the full emitted signal), i.e., some or all of the modulation applied to the emitted signal must be known in advance at the collection platform. Conventional array-based multi-emitter geolocation techniques also exist that rely on use of multiple separate simultaneous collection platforms such as separate aircraft.
Other existing array-based direction finding systems exist that can locate multiple cochannel emitters using intermediate geolocation observable measurements. One conventional geolocation approach generates multiple line-of-bearing (LOB) measurements (hard decisions), and then estimates position based on these observables. Several algorithms exist to generate LOBs in a co-channel environment (e.g., such as MUSIC, MVDR). Conventional observable-based geolocation techniques typically become impossible with low-SNR emitters and overloaded environments (i.e., environments with more signals than antenna elements). Conventional observable-based geolocation techniques are also sub-optimal in the sense that hard decisions are made on small blocks of data, without considering the spatial correlation of the emitters.